Conventional golf balls can be divided into two general types: two-piece balls and threepiece balls (also known as wound balls).
Two-piece balls are made with a one-piece compressible, resilient core encased by a cover material. The core is usually made of a compression- or injection-molded cross-linked rubber such as a chemically cross-linked polybutadiene and has about the same size as a wound core, i.e., approximately 1.45 to 1.61 inches in diameter. The cover is generally injection molded or compression molded about the core and may be comprised of a urethane material, a synthetic balata rubber material, or a blend of ionomer resins, such as the various grades of ionomer resins produced by DuPont which are trademarked SURLYN, or the various types of ionomer resins produced by EXXON CHEMICAL which are trademarked IOTEK.
Three-piece balls, also known as wound balls, typically have either a solid rubber or liquid-filled bladder center core which may vary in diameter from 3/8 of an inch to 11/16 inches. Such center cores are then tightly wound with elastic thread to form a complete core which may have a diameter of approximately 1.45 to 1.61 inches. The complete wound core is then covered with a urethane, balata, ionomer, or similar material. The cover material is usually either compression molded or injection molded around the wound core to form a final ball that typically measures 1.68 inches in diameter. As a result of their more complex structure, wound balls generally require a longer time to manufacture and are more expensive to produce than one- or two-piece balls.
Multi-piece golf balls are also known and come in various forms. For example, a golf ball has been disclosed that includes at least five parts including a three-part solid core having a center section surrounded by two outer layers molded one about the other, each made of a elastomeric material to form the entire center core, and two cover layers made up of differing blends of ionomer type resins wherein the inner cover layer may be harder or softer than the outer dimpled cover layer. Purportedly, this ball travels a satisfactory distance and may have its coefficient of restitution, feel, and spin rate adjusted by changing the chemical composition of the various polymer blends that make up its multi-piece core and covers.
Golf balls are also disclosed that contain either one-piece solid cores or two-piece wound cores with two or more layers of cover material. The harder inner cover layers of these balls purportedly increase the coefficient of restitution of these balls and promote increased travel, and the softer dimpled outer covers purportedly increase the softer feel and the spin rates of these balls.
Other golf balls are also disclosed that contain solid spherical metal cores, metal cores of various shapes and diameters, and cores containing steel balls; the purpose usually being to increase the ball's flight (also referred to as travel or distance) and to create more accurate flight. Such prior art golf balls, however, are impractical because they are too expensive to manufacture, and have undesirable characteristics such as heavy centers and lighter exteriors which increase the spin rates of these balls to undesirable levels, or because their design would not be sanctioned by the United Sates Golf Association for use in tournament play.
A ball incorporating a resilient, springy, perforated metal sphere near its outer circumference to maintain the shape and integrity of a cover made of unstable gutta-percha and prevent the gutta-percha from becoming misshapen when struck with a golf club is also known, and is described in U.S. Pat. No. 705,249. Gutta-percha, a tree sap in its natural gum form, was utilized as a golf ball cover material in the late 1800s and early 1900s. By reason of being mounted just beneath the surface of the gutta-percha cover whereby portions of the gutta-percha were forced into the perforations, the flexible, springy, perforated metal shell of this golf ball served to reinforce the unstable gutta-percha cover and help it from becoming misshapen when struck with a golf club, rendering the ball dead under a light blow. Col. 1, 11. 49-51.
It should be noted that all known golf balls may be made larger than (but not smaller than) the accepted 1.68 inch diameter size and still be approved for tournament play by the United States Golf Association.
There remains a need for a multi-piece, three piece, two-piece, or one-piece ball that has longer travel relative to its compression.